The present invention relates to a system for the detection of objects in a body of water, and more particularly, to the display of underwater acoustic sensor system data.
Surveillance of bodies of water for military and commercial applications include the art of underwater sound detection. Underwater acoustic sensing devices, such as sonar buoys, are often deployed to aid in the surveillance operations including harbor defense, smuggling countermeasures, riverine observation, force and vessel protection. Passive sonar buoys sense sounds, such as those sounds produced by propellers and machinery. Active sonar buoys bounce a sonar signal off the surface of an object, such as a vessel. Detection of small, shallow-draft surface crafts at high speeds in shallow or very-shallow water is the most difficult surveillance problem.
Sonar buoys typically include a buoyant chamber containing one or more sensors, such as hydrophones, and a transmitter. Hydrophones convert underwater sound pressure waves to electrical signals. The acoustic surveillance system attempts to ascertain bearing and signature information from the pressure waves received. Bearing information includes azimuth, and possibly elevation, to the target relative to the sensor and is ascertained using hydrophone sensors with orthogonally-oriented axes. Signature information involves identifying characteristics, such as frequency, of detected sounds.
Sound signals are amplified and transmitted to a surveillance acoustic processor. The transmitted signal is a composite of the signals received by the various sensors. Signal transmission may be via radio frequency or cable. The complex underwater sound electrical signal is further processed by the acoustic processor to obtain sound source discrimination which is finally displayed for operator interpretation. Conventionally, sensor sound signal data was displayed in graph form versus time. Optionally, historical data was displayed along with the most recent sensor information to facilitate pattern recognition.
Acoustic surveillance system operators must quickly compare and correlate bearing and signature information to identify and locate objects in the water. This is particularly difficult in shallow or very shallow water, where objects are only detected close to the sensor, thus bearing and signature information change quickly. Multiple targets further complicate the operator""s task.
Some conventional acoustic surveillance systems display only signature, i.e., frequency history, information, when bearing information is not available. FIG. 1 is a pictorial representation of such a conventional frequency history acoustic data display. Where bearing history information is available, frequency history and bearing history are conventionally displayed side-by-side as illustrated in FIG. 2. Time extends downward along the vertical axis of a conventional display. The most recent data is located at the top of the display. In this orientation, the time axis of the bearing history portion is aligned in parallel with the time axis of the frequency history portion. In this manner, the operator relates events on the frequency history with events occurring at the same time on the bearing history. Optionally, a conventional acoustic surveillance system display presents multiple copies of the frequency history for sensors in different directions.
The manner in which a conventional acoustic surveillance system displays frequency history and bearing history sensor data burdens the system operator with the task of relating the various frequency history traces to one or more of the various bearing history traces. If a target suddenly turns itself off, the operator sees both frequency trace lines and bearing trace lines stop, enabling the operator to relate the two traces. When a target performs an abrupt maneuver, typically an operator observes a dramatic shift in bearing along with a change in frequency of the associated signal, again enabling a relation of signals.
In the fast-paced environment of shallow-water acoustic surveillance, multiple frequency and bearing traces, each potentially changing with time, make the operator""s relational task complex and difficult. Since the operator performs the significant portion of the relational computations involved in interpreting a conventional display, constant vigilance and quick action are necessary with conventional shallow water acoustic surveillance applications.
To avoid the shortcomings of the above-discussed techniques and for other reasons presented in the Description of the Preferred Embodiments, a need exists for an acoustic surveillance system which displays target data in a more efficient manner so that an operator can instantly distinguish and correlate between the signatures for targets at different bearings.
The present invention provides an acoustic surveillance system and method including a user interface for graphically displaying acoustic information produced by acoustic surveillance system sensors. The acoustic surveillance system user interface includes a processor and an acoustic data display. The processor receives the acoustic information from the acoustic surveillance system sensors and provides graphical display information representative of the acoustic information. The acoustic data display is coupled to the processor for receiving the graphical display information and includes a frequency history display area having a frequency axis and a time axis, a bearing history display area having a bearing axis and a time axis, and a frequency/bearing display area having a frequency axis and a bearing axis.
In one embodiment, the frequency axis of the frequency/bearing display area is the same as the frequency axis of the frequency history display area and the bearing axis of the frequency/bearing display area is the same as the bearing axis of the bearing history display area.
In a preferred embodiment, the frequency history area of the display is located above the frequency/bearing display area and the bearing history display area is located to the left of the frequency/bearing display area of a single s degrees to 360 degrees are provided on the display. In one embodiment, the display identifies the acoustic surveillance system sensor displayed.
In one embodiment of the invention, DIFAR sensors receive underwater sound pressure waves and provide electrical sound data signals which are transmitted to the processor.
In one embodiment, a marker located within the frequency/bearing display area identifies the computed bearing associated with an identified frequency. Relative directional uncertainty of the computed bearing is indicated by the width of the marker. In an alternate embodiment, uncertainty is indicated by marker size.
The present invention provides, in a single display, a frequency/bearing display area to efficiently show the correlation between the frequency/time history and bearing/time history information to the operator in an easy-to-interpret manner. The three display areas of the display are arranged and orientated so that the operator can instantly distinguish between the signatures for targets at different bearings. In addition, the historical bearing and signature information allows an operator to quickly recognize new targets.